Ducted wind turbine and support platform

ABSTRACT

The invention relates to a ducted wind turbine having a turbine rotor assembly which extracts kinetic energy from air flowing there past. The rotor assembly includes a plurality of rotor blades having rotor tips at their outermost ends which define a rotor tip sweep circumference. A duct assembly at least partially surrounds said rotor tip sweep circumference and a base platform supports the ducted wind turbine. The duct assembly is mounted on the base platform by way of a weathervane bearing arrangement such that the duct assembly may weathervane around the turbine rotor assembly in response to changes in wind direction. A semi-submersible support platform, wave energy capture apparatus, torsional bearing mechanism and a latticework wind turbine tower associated with the ducted wind turbine are also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national phase application under 35 U.S.C. §371 of International Application No. PCT/GB2017/053186 filed on Oct. 20,2017, which claims priority to Great Britain application no. 1617803.0filed on Oct. 21, 2016, the entire disclosures of which are herebyincorporated by reference in their entirety for all purposes.

The present invention relates to a ducted wind turbine, particularly,but not exclusively, a floating ducted wind turbine for use in offshoreenvironments. A semi-submersible support platform, wave energy captureapparatus and a torsional support bearing for use with or without theducted wind turbine is also described.

In recent years there has been an increased demand for electricitygenerated by renewable energy sources such as wind turbines. With this aconsequential increased demand for efficiency in such turbines has ledto turbines being developed with increasingly longer blade lengths. Forexample, wind turbines having a blade length of over 80 metres, and anassociated power generation capacity in the region of 8 MW exist.

However, it is generally accepted that the size and power generatingcapacity of such turbines cannot continue to increase. This is due tothere being numerous factors which are likely to eventually placeeffective limitations on the size and power generating capacity of suchturbines; for example, materials engineering may not continue to providematerials which are able to withstand the aerodynamic, dynamic andstatic forces placed upon such large structures; socio-politicalpressures may make the erection of such large turbines impossible; otherlogistical/manufacturing reasons may make such structures non-viable/tooexpensive.

Offshore wind, wave and tidal turbines have been developed with a viewto addressing these and other issues; however, many such turbines havepoor survivability prospects in the inherently harsh environmentalconditions likely to be experienced during their power generatinglifetime. Indeed, it is the largest amplitude waves and strongest windsthat have the potential to generate the most electrical power in suchdevices; however, many known systems require to be shut down, parked orotherwise secured during such conditions to avoid being damaged.

According to a first aspect of the present invention there is provided aducted wind turbine comprising:—

-   -   at least a turbine rotor assembly adapted to extract kinetic        energy from air flowing there past, the rotor assembly        comprising a plurality of rotor blades having rotor tips at        their outermost ends which define a rotor tip sweep        circumference;    -   a duct assembly at least partially surrounding said rotor tip        sweep circumference;    -   a base platform adapted to support the ducted wind turbine; and    -   wherein the duct assembly is mounted on the base platform by way        of a weathervane bearing arrangement such that the duct assembly        may weathervane around the turbine rotor assembly in response to        changes in wind direction.

The ducted wind turbine may comprise a base platform for flotation onwater. Said base platform may comprise a semi-submersible base platform.

A ducting channel may be provided between a ducting inlet and a ductingoutlet of the wind turbine assembly, each ducting inlet and outlethaving a longitudinal axis. The ducting inlet and outlet may be arrangedsuch that their respective longitudinal axes are substantially parallelyet vertically or laterally offset relative to one another. The ductinginlet and outlet may alternatively be arranged such that theirrespective longitudinal axes intersect with one another at a redirectangle α.

The redirect angle α may be between around 90 to 170 degrees.

The area of the ducting inlet and outlet may be substantially equal toone another in order to minimise compression or expansion of air flowingthrough the wind turbine.

The area of the ducting inlet may be greater than the area of theducting outlet in order to create a ram effect on air passing throughthe turbine.

The area of the ducting inlet may be lesser than the area of the ductingoutlet in order to create a diffuser effect on air passing through theturbine.

The ducting inlet and the ducting outlet may comprise a circular, ovoid,or rectangular shaped area.

The ducting channel may comprise at least a guide vane arrangementadapted to guide air flow through the ducting channel and into theturbine rotor assembly.

A plurality of turbine rotors in the turbine rotor assembly may beassembled on two sets of coaxial contrary rotating hubs such that aprimary set of rotors rotating in one direction and a secondary set ofrotors rotating in an opposite direction may be provided.

The inner surface of the ducting channel may be aerodynamicallyoptimised to facilitate smooth flow of air flow therethrough withminimal energy losses.

The outer surface of the ducting channel may aerodynamically optimisedto minimise structural loads and aerodynamic turbulence on the turbineand semi-submersible base platform while enhancing air flow andpromoting lower pressure across the ducting outlet and adding momentumto flow exhausted from the turbine outlet in order to aid the turbinemass air flow and energy capture.

The wind turbine arrangement may be provided with a vertical stabilisertail either integrated with or separated from yet connected to, theducted wind turbine in order to facilitate said weathervane movement.The tail may comprise steerable control surfaces and/or trim tabs.

The semi-submersible base platform may comprise a delta wing shapedarrangement having a plurality of discrete flotation members extendingdownwardly therefrom.

The semi-submersible base platform may comprise four discrete flotationmembers, one being provided at or toward each corner of thesemi-submersible base platform such that a fore flotation member, an aftflotation member and two flanking flotation members may be provided.

Each of the discrete flotation members may comprise a lower float memberattached to the semi-submersible platform by way of a support struthaving a small hull cross sectional area at the water surface in orderto maximise the stability of the support provided.

The weathervane bearing arrangement may comprise a substantiallycircular load bearing plate and a corresponding substantially circularrecess provided between the wind turbine arrangement and thesemi-submersible base platform such that, in use, the duct assembly mayweathervane around the turbine rotor assembly.

The weathervane bearing arrangement may further be provided withfriction reducing means in order to facilitate loaded rotationalmovement of the duct assembly relative to the semi-submersible baseplatform in response to movements in the prevailing wind direction.

A plurality of wave energy absorbers may extend from an attachment pointon the semi-submersible base platform to the water such that one end ofeach wave energy absorber may be directly or indirectly supported by thebase platform and the other end may be supported by buoyant engagementwith the water.

Said wave energy absorbers may extend rearward from a trailing edge ofthe semi-submersible base platform on either side of the turbinearrangement.

Said attachment points of the wave energy absorbers may be arrangedprogressively rearward on the semi-submersible platform such that, inuse, a wave passing the wind turbine arrangement will progressivelyinteract with the forwardmost to rearmost wave energy absorbers insuccession.

The wave energy absorbers may be provided with an energy flotationmodule for buoyant interaction with the water.

The energy flotation module may comprise a substantially semi-sphericalflotation member provided at a distal end of a structural arm of thewave energy absorber.

The energy flotation module may comprise a combined monocoque structuralarm and flotation chamber.

The wave energy absorbers may be attached to the semi-submersibleplatform by way of a torsional bearing arrangement comprising a firstrotatable member, a second rotatable member in rotatable communicationwith the first rotatable member, and torsional resistance means providedbetween the first and second rotatable members such that when at leastone of the rotatable members is rotated relative to the other rotatablemember a torsional resistance to such movement is created between saidrotatable members.

At least a water turbine arrangement may be supported below the watersurface by the semi-submersible platform.

A diffuser arrangement adapted to improve air flow through the turbinerotor assembly may also be provided.

According to a second aspect of the present invention there is provideda semi-submersible support platform comprising:

-   -   an upper support deck upon which items, machines, buildings,        equipment or other items may be sited;    -   a plurality of lower discrete flotation members;    -   a plurality of corresponding support struts extending from each        corner of the support deck to each corresponding flotation        member, the support struts having a cross sectional area which        is small relative to that of the flotation members in order to        maximise the stability of the support provided thereby to the        upper support deck;    -   an anchoring arrangement provided at a leading corner of the        support deck in order to allow the support platform to        weathervane there around and to thereby create a fore flotation        member, an aft floatation member and two flanking flotation        members.

A weathervane bearing arrangement may be provided such that the ductassembly may weathervane with respect to the semi-submersible baseplatform in response to changes in prevailing wind direction.

The wind turbine assembly may comprise a ducted wind turbine.

The wind turbine assembly may comprise a ducted wind turbine having aducting channel provided between a ducting inlet and a ducting outlet ofthe wind turbine assembly, each ducting inlet and outlet having alongitudinal axis. The ducting inlet and outlet may be arranged suchthat their respective longitudinal axes are substantially parallel yetvertically or laterally offset relative to one another. Alternatively,the ducting inlet and outlet may be arranged such that their respectivelongitudinal axes intersect with one another at a redirect angle α.

The redirect angle α may be between around 90 to 170 degrees.

The upper support deck may be adapted to site a nuclear reactorfacility.

The upper support deck may comprise a delta wing shaped arrangement.

A plurality of wave energy absorbers extending from an attachment pointon the semi-submersible base platform to the water such that one end ofeach wave energy absorber is directly or indirectly supported by thebase platform and the other end is supported by buoyant engagement withthe water may be provided.

At least a water turbine arrangement supported below the water surfaceby the semi-submersible platform may be provided.

According to a third aspect of the present invention, there is providedwave energy capture apparatus comprising:

-   -   a support platform providing an attachment and pivot point for        the wave energy capture apparatus;    -   an elongated arm member attached to the support platform, the        elongated arm member comprising a monocoque buoyant float for        buoyant interaction with a passing wave such that it may rotate        around said pivot point in response to said passing wave.

According to a fourth aspect of the present invention, there is provideda torsional bearing mechanism comprising:

-   -   a first rotatable member;    -   a second rotatable member in rotatable communication with the        first rotatable member; and    -   torsional resistance means provided between the first and second        rotatable members such that when at least one of the rotatable        members is rotated relative to the other rotatable member a        torsional resistance to such movement is created between said        rotatable members.

The torsional resistance member may comprise a metallic or non-metallicrod.

Additional substantially non-torsional support members may be providedbetween the first and second rotatable members in order to structurallysupport said members during rotation relative to one another.

According to a fifth aspect of the present invention there is provided alatticework wind turbine tower comprising:

-   -   an outer circumferential face;    -   a corresponding inner circumferential face; and    -   a plurality of cross brace structural members provided between        the outer and inner circumferential faces.

The outer and or inner circumferential faces may comprise a plurality ofcurved or straight structural brace members.

The latticework turbine tower may comprise an aerodynamic coveringprovided over and between the structural brace members of thelatticework.

Further features and advantages of the present invention will becomeapparent from the claims and the following description.

Embodiments of the present invention will now be described by way ofexample only, with reference to the following diagrams, in which:

FIGS. 1A and 2 are schematic perspective side view illustrations of aducted wind turbine mounted on an associated semi-submersible platformin accordance with a first embodiment of the invention;

FIG. 1C is a schematic perspective side view illustration of a floatingducted wind turbine in accordance with a second embodiment of theinvention;

FIG. 1B is a schematic transverse illustration of an alternative linkedfloatation hull arrangement;

FIG. 3A is a schematic plan view illustration of the turbine of FIGS. 1Aand 2;

FIGS. 3B and 3C are schematic plan views of example alternatively shapedsupport platform and flotation arrangements;

FIG. 4A is a transverse partial cross sectional schematic illustrationof the turbine of FIGS. 1A and 2;

FIG. 4B is a transverse partial cross sectional schematic illustrationof the turbine of FIG. 1C;

FIG. 5 is a more detailed schematic illustration of a turbine blade, huband internal tower arrangement of the turbine of FIGS. 1A and 2;

FIG. 6 is a more detailed schematic illustration of an alternativeembodiment of the turbine where the internal tower profile has anarrowed cross section;

FIG. 7A is a more detailed schematic front illustration of a railwayaxle and associated railings of FIGS. 5 and 6;

FIG. 7B is a plan view schematic illustration of the arrangement in FIG.7A;

FIG. 8A is a schematic plan view illustration showing a turbine tower inaccordance with an alternative embodiment where two example turbineblade formations are illustrated attached thereto;

FIG. 8B is a schematic perspective view illustration showing a portionof the turbine tower of FIG. 8A;

FIG. 8C is schematic perspective view illustration showing an upperportion of the turbine tower of FIG. 8A in greater detail;

FIG. 9A is a lower perspective schematic illustration of an alternativewave energy absorber attached to a torsional bearing arrangement;

FIG. 9B is a more detailed illustration of the torsional bearingarrangement of FIG. 9A;

FIG. 10 is a schematic diagram illustrating the basic principle ofoperation of the wave energy absorber;

FIG. 11 is a perspective illustration of the arrangement in FIG. 3 wherea pair of additional inclined axis water turbine arrangements extendfrom the trailing edge of the arrangement;

FIG. 12A is a more detailed plan view schematic illustration of aninclined axis water turbine arrangement and its associated components;and

FIG. 12B is a transverse schematic illustration of the arrangement shownin FIG. 12A.

With particular reference to FIGS. 1 to 3 an offshore power generatingmodule generally designated 10 comprises a floating ducted wind turbine(DWT) generally designated 12 mounted upon a semi-submersible platform(SSP) generally designated 14.

The DWT 12 comprises a contoured and shaped outer cowl 16 which isaerodynamically contoured on its inner side to facilitate smooth flow ofair flow therethrough with minimal energy loss, and aerodynamicallycontoured on its outer side to minimise structural loads and aerodynamicturbulence on the DWT 12 and the SSP 14 upon which it is mounted.Downstream from the cowl 16 is an intermediate empennage section 18which tapers from the cowl 16 to an associated vertical stabiliser 20.

Several types and format of material may be utilised in order to formthe cowl 16, empennage 18 and tail 20 section; however, examples includesail cloth, fibreglass, geodetic structures etc.

The outer cowl 16 gradually and aerodynamically tapers from arectangular section inlet duct 22 at its in use front end to a circularsection outlet duct 24 at its upper surface. Tapered cut-outs (notshown) may be provided in the side walls of the cowl 16 adjacent theinlet 22 in order to facilitate entry of any off-centred gustsencountered. As shown in FIG. 4, the inlet duct 22 is provided with alongitudinal axis L1 and the outlet duct 24 is provided with alongitudinal axis L2. In conforming from the rectangular shaped sectionadjacent inlet duct 22 to the circular shaped section adjacent outletduct 24, the cowl 16 turns through a redirect angle α (FIG. 4) thisbeing the angle between the two axes L1 and L2. In the embodimentillustrated this redirect angle α is in the region of 100 degrees;however, it may be far lesser or greater depending upon requirements.

As best illustrated in FIGS. 2 and 4A, the internals of cowl 16 alsocomprises a series of horizontally arranged air flow guide vanes 26 anda central vertically arranged air flow baffle 28.

With particular reference to FIG. 4A, inside the DWT 12, a main air duct25 is provided and the guide vanes 26 are gradually curved from theinlet longitudinal axis L1 toward the outlet longitudinal axis L2 inorder to similarly direct the flow of air passing therethrough. Thevertical separation distance between the guide vanes 26 also graduallyincreases as they progress from the inlet duct 22 toward the outlet duct24 in order to promote smooth airflow and facilitate an evendistribution of air toward the outlet 24. An optional diffuser wing 27may be provided at a suitable distance above the DWT outlet 24 in orderto advantageously interact with the airflow exhausted therefrom in orderto maximise the efficiency of the apparatus (as represented by lines Fin the area D in FIG. 4A). The upper surface of the diffuser wing 27 mayalso be provided with an array of photovoltaic cells in order to allowfurther energy capture from solar energy if desired.

A contra-rotating turbine assembly (CRTA) 30 projects into the main airduct 25. With reference to FIG. 5, the CRTA 30 includes a primary set ofturbine blades 32 and a secondary set of turbine blades 34 which arearranged such that they are contra-rotating relative to one another. Theprimary blades 32 are mounted upon a primary tower 36 and the secondaryblades 34 are mounted upon a secondary tower 38 which is coaxiallysurrounded by the primary tower 36 (the primary and secondary towers areshown in partial cut away section for illustrational purposes in FIG.5). With the blade orientation illustrated in FIG. 5, the primary bladeswill rotate in the clockwise direction (when viewed from above) and thesecondary blades will rotate in an anti-clockwise direction (when viewedfrom above) when the airflow A passing through the DWT 12 is imparted onthem; however, these directions may be altered by changing the bladeorientations as desired. Furthermore, an active blade pitch adjustmentmechanism may be utilised if desired.

With reference to FIG. 6, in an alternative embodiment, the crosssection of the main air duct 25 at or adjacent the CRTA 30 may comprisea narrowed section in order to provide altered flow dynamics representedby arrows A1 through the DWT 12.

In the embodiments illustrated by FIGS. 5 and 6, the primary andsecondary sets of blades 32, 34 are not rotationally mounted on theirrespective towers 36, 38. Instead the sets of blades 32, 34 are rigidlymounted to their respective towers 36, 38 and the towers 36, 38 arerotationally mounted on their respective bases at a power deck module40. However, in an alternative embodiment, the reverse can be achievedby locating the bearings and electricity generators (discussedsubsequently) at the same height as the turbine blades atop the towersif required.

In the embodiment illustrated in FIGS. 5 and 6, the towers 36, 38comprise a latticework space frame structure having curved membersarranged so as to provide a circular outer cross section; however, anyalternative structure may be utilised as appropriate.

With reference to FIG. 8A, in an alternative embodiment a turbine tower136 (which may be a primary or secondary turbine tower) comprises amulti-faceted latticework space frame structure. In the embodimentillustrated the cross section of the structure is shown as beinghexagonal; however, any number of straight sides may be provided inorder to form the required 360 degree formation of the tower. Each cellof the latticework comprises an outer face strut 136A, inner face strut136B, and diagonal cross bracing strut 136C. Where for example thelengths of the outer face struts 136A are in the region of 6 metresaround 40 flat faces may be provided around the circumference of thetower 136 in order to provide a 360 degree assembly.

With reference to FIG. 8B, each cell of latticework is mounted upon andadjacent to similarly arranged cells in order to provide a double walledmulti-faceted latticework tower.

With reference to FIG. 8C, turbine blades 132 are attached to the cellsof the tower 136 by way of one or more blade root rods 135. In use, whenthe turbine blade is driven in the direction indicated by arrow A inFIG. 8C the blade root rod 135 creates a coupled force T1 and T2 andimparts a rotational force F on the tower 136 which in turn generateselectrical power by driving electricity generating modules (not shown).

The lattice framework arrangement described with reference to FIGS. 8Ato 8C minimises the primary and/or secondary tower overall mass,material and construction costs.

The structures referred to above may be provided with a drag reducingaerodynamic skin if required in order to minimise disruption to the airflowing there past within the main duct of the DWT 12.

Referring again to FIGS. 5 and 6, the power deck module 40 comprises aprimary set of roller bearing assemblies 42 and a primary electricitygenerator 44 which are associated with the primary tower and hence theprimary blades 32. Likewise, for the secondary tower 38 the power deckmodule 40 also comprises a secondary set of roller bearing assemblies 46and a secondary electricity generator 48 which are associated with thesecondary tower and hence the secondary blades 34.

With reference to FIGS. 7A and 7B, the roller bearing assemblies 42, 46comprise a pair of wheel sets 48 which are located within a bogeyarrangement 50 by resilient spring/damper arrangements 52 in order toallow the wheel sets 48 to follow a circular curved section ofassociated track 54.

The electricity generators 44, 48 comprise any suitable generator suchas for example a large diameter permanent magnet and coil generator.

With reference to FIG. 1A, the SSP 14 comprises a square planar uppersupport deck 56 having a pair of trailing wings 58 extending rearwardfrom opposing corners of the deck 56 in order to form a resultantdelta-wing shape when anchored by a tether diagrammatically representedby arrow 60 in FIG. 1A.

Note that in alternative embodiments illustrated by FIGS. 3B and 3C, theSSP 14 and any associated flotation arrangement may be arranged withalternatively shaped profiles depending upon requirements.

Returning to the arrangement of FIG. 1A, four hull support struts 62project downwardly from the support deck 56 toward correspondingflotation hulls 64 provided with heave plates 66. The relativedimensions of the support struts 62 and the dimensions/buoyancy of theflotation hulls 64 are dimensioned such that the support struts 62 havea relatively (in relation to the buoyancy provided by the hulls 64) lowcross sectional area at the point at which they are likely to meet thewaterline in order to maximise the stability of the support provided inaccordance with “Small Waterplane Area Twin Hull” (SWATH) theory. Atypical expected mean position of the waterline is indicated as W inFIG. 4A. More or less than four hull support struts may be provideddepending upon requirements.

With reference to FIG. 1B, in an alternative embodiment, the floatationhulls 64A may be linked to one another by link 65 and connected to theSSP 14 by one or more supports struts 62A as desired. The link 65illustrated in FIG. 1B is shown in-line with the longitudinal axes ofthe floatation hulls 64A; however, in an alternative embodiment (notshown) the link may instead be linked perpendicular to the linkedfloatation hull longitudinal axes.

Extending rearward from the trailing wings 58 are several wave energyabsorbers 68. These are of the same length as one another so that theirends effectively mirror the delta-wing shape of the trailing wings 58for purposes which will be described subsequently. The wave energyabsorbers 68 comprise elongated arms 70 which are connected to thetrailing wings 58 at one end by a pivot joint 72 and provided with asemi-spherical flotation arrangement 74 at the other end for engagementwith the water surface/passing waves.

With reference to FIGS. 9A and 9B, in an alternative embodiment, thewave energy absorbers comprise a combined monocoque structural arm andflotation chamber arrangement 68A having a torsional bearing 80 andpower take off connections 78 at one end thereof. The torsional bearing80 is provided to allow pivoting attachment of the flotation chamber 68Ato the SSP 14 and comprises a central disc 76 which is rigidly connectedto the flotation chamber 68A, a pair of end discs 82 which are rigidlyconnected to an appropriate anchoring point on the SSP 14, andtorsional/supporting rods 84 which connect the end discs 82 to thecentral disc 76.

Referring to FIGS. 1 to 3, the DWT 12 is attached to the SPP 14 by wayof a rotating table arrangement generally designated 86 and comprising acircular load bearing plate 88 attached to the underside of the DWT 14and a corresponding circular recess 90 provided on upper deck 56 of theSSP 14. Friction reducing means such as e.g. wheel and trackarrangements similar to the roller bearing assemblies 42, 46 describedabove, or e.g. ball bearing based arrangements provide the DWT 12 withthe ability to weathervane upon the SSP 14 as indicated by arrow W inresponse to changes in the prevailing wind direction.

In the described embodiments the height of the overall combined DWT andSSP structure might be in the region of around 200 to 800 metres withthe wing span from tip to tip also being in the region of around 200 to800 metres; however, the reader will appreciate that these dimensionsmay be greatly altered to suit the predicted forces, power generatingrequirements, deployment location etc. as required.

The offshore power generation module 10 may also be provided with tidalturbine arrangements such as vertical “across” axis turbines (asdiagrammatically illustrated by 75 in FIG. 3) horizontal “across” axisturbines, or axial flow turbines (as diagrammatically illustrated by 90in FIGS. 12 and 12A, 12B.

With reference to FIGS. 12A and 12B, a combined turbine a main turbineshaft 92 is angled into the water from the SSP 14 and is provided with aturbine arrangement 94 at its lower end. The main shaft 92 and/orturbine 94 are buoyant such that any heave loads are minimised and suchthat radial bearing loads are reduced at the hub/pivot point. Thisbuoyancy also supports the turbine mass and reduces any bending momentapplied to the main shaft in order to reduce fatigue loads resultingfrom the shaft rotation. The flow into the turbine is also augmentedinto the turbine by fairings 96.

In use, the offshore power generating module 10 is first towed into itsdesired waterborne operating location either by a suitable vessel or bya self-propelling motor etc. This location may be at shallow or deepwater sea, rivers, estuaries, or on inland water features such as lakes,and inlets etc.

Once at a suitable location, the module 10 is tethered there by anysuitable anchoring arrangement as diagrammatically represented by arrow60 in FIG. 1A. In such a condition the prevailing water current impartedon the SSP 14 will naturally cause it to weathervane around its tethersuch that the SSP 14 will naturally align with the prevailing watercurrent.

As a prevailing wind (which may be in a different direction from theprevailing water current) is imparted upon the DWT 14 the force of saidwind will interact with the intermediate empennage section 18 andvertical stabiliser 20 in order to naturally cause the front of the DWT14 cowl 16 to weathervane on its bearing table 86 around the turbinemodule into the wind as illustrated by arrow W in FIG. 1A.

In this way the SSP 14 will always naturally be aligned with theprevailing water current and the DWT 12 will always naturally be alignedwith the prevailing wind direction.

Alternatively, or additionally, the orientation of the DWT 12 cowl 16relative to the prevailing wind direction may be controlled activelyusing a forward looking sensing system. An example such system is LIDARwhere LIDAR sensors are provided on or around the cowl 16. In such anarrangement, sensing data is processed by on board or remote computercontrol systems and sends control responses to electro-mechanical,pneumatic, magnetic and/or hydraulic actuators in order to eitherdirectly drive the wind turbine cowl 16 into the wind or cause thecomponents of the tail 20 to deflect and therefore cause the cowl 16 torotate into the wind.

Such control systems may in some circumstances allow the cowl 16 torespond more quickly to wind direction changes than might be the casewith passive weathervane control alone. The above control systems may beused in addition or independently to control or adjust any aerodynamicor other system anywhere within the system.

The provision of LIDAR sensors in conjunction with such a control systemalso allows oncoming wave and swell sea states and profiles which mayinterface with the power generating module 10 to be detected. When suchexpected conditions are detected this information is input to the systemsuch that all responses of any components can be optimised to ensure amaximum efficiency of energy harvesting from the environment by thesystem's various components. For example, the resistance to movement ofthe wave energy absorbers can be increased when high magnitude waves areexpected. This may also enhance platform stability and reduce mechanicaland electrical stresses throughout the system as a whole which in turnmay help to extend the lifetime of the system and reduce maintenancerequirements.

Such control systems and software may be pre-programmed or containlearning algorithms. Control input requirements may be generated onboard the power generating module 10, at an operator control centre orfrom demand side inputs (for example electricity grids or energycompanies).

With reference to FIG. 4A, with the duct inlet 22 of the DWT 12 facingdirectly into any prevailing wind, incoming airflow A will enter themain air duct 25 of the DWT through the inlet 22, travel along and upthe internal main duct 25 under the guidance of the guide vanes 26, andwill be directed upwards towards the turbine arrangement 30.

With reference to FIG. 5, when such ducted airflow A meets the primaryset of turbine blades 32 it will impart a clockwise (when viewed fromabove) rotational force thereupon. Since the primary blades 32 aremounted on primary tower 36 which itself is mounted upon wheel bearings42 the primary tower 36 will rotate under the action of said rotationalforce. As this occurs electrical power will be generated at the primarygenerator 44.

In a similar fashion, once the stream of air has passed the primary setof turbine blades 32 it will impart upon the secondary set of turbineblades 34 and hence impart a rotational force thereon. However, sincethe secondary blades 34 are orientated in the opposite sense from theprimary blades 32 this will be an anti-clockwise (when viewed fromabove) rotation force. Since the secondary blades 34 are mounted onsecondary tower 38 which itself is mounted upon wheel bearings 46 thesecondary tower 38 will rotate under the action of said anti-clockwiserotational force. As this occurs electrical power will also be generatedat the secondary generator 48.

Throughout the above described operations, it will be appreciated thatthe duct or cowl assembly 16 is free to weathervane around the turbinearrangement without any rotation of the turbine rotor assembly as awhole being required. This creates a useful mechanical dissociationbetween the angular orientation of the duct or cowl assembly 16 from theangular orientation of the remaining components of the power generatingmodule 10.

The previously described contra-rotation of the primary blades 32relative to the secondary blades 34 means that any torque generated byone set of blades is, in the most part, cancelled out by any torquecreated by the other set of blades. This results in minimum residualtorque being applied to the SSP 14 upon which the DWT 12 is mounted.

The process of harvesting energy from the water upon which the SSP 14 isstationed will also now be described. For clarity this will be describedwith reference to an example passing wave and separately with referenceto an example prevailing water current; however, it will be appreciatedthat the module is capable of harvesting energy from the wind, waves andwater current simultaneously.

As an example wave approaches the module 10, its first usefulinteraction with it will be with the semi-spherical flotationarrangements 74 of the two foremost wave energy absorbers (e.g. the twowave energy absorbers nearest to the centreline of the SSP 14). Withreference to FIG. 9 as wave front W travelling in direction A interactswith the float 74 the float's inherent buoyancy will rotate the float 74and its attached arm 70 upwards away from its neutral position (whereits longitudinal axis is in position P1) towards its loaded position(where its longitudinal axis is in position P2). During such rotationaway from the neutral position P1, the buoyant force of the float 74acts to apply a torsional loading force to the torsional bearing 80 andto usefully move any power take off arrangements attached to the powertake off connections 78 thereof and hence generate power. This loadingof the torsional bearing 80 essentially stores a portion of the kineticenergy harvested from the upward motion of the wave energy absorber 68as potential energy within the torsional bearing 80. The reluctance ofthe SSP heave plates 66 to vertical movement within the water columnalso provides a reaction force against which the floats 74 act duringthis up-stroking loading phase.

Once the float 74 has reached the crest of the wave front W the arm 70will be in position P2 and the torsional bearing 80 can be considered asfully loaded for that wave front W. At this point, the wave front Wbegins to fall away and no longer fully support the weight of the waveenergy absorber 68 such that the wave energy absorber 68 will begin toride back down the crest of the passing wave front W. Whilst doing so,the potential energy stored within the torsional bearing 80 is releasedthereby facilitating said down stroking of the wave energy absorber 68.

The above described transfer of kinetic energy from the up-stroking waveenergy absorber 68, to temporarily stored potential energy in thetorsional bearing 80 and then back to kinetic energy in thedown-stroking wave energy absorber 68 is (with the exception of powerusefully extracted by the energy take offs) substantially energyneutral; however, this provides a strong support bearing having thedesired pivoting abilities with minimal frictional losses.

Since wave profiles can generally be approximated as a mathematical sinewave, the movement profile and hence electrical power generation profileof each wave energy absorber 68 can also be generally approximated to amathematical sine wave. As a given wave passes each wave energy absorber68 additional sine wave energy profiles are created. This creates a setof phase-shifted energy pulses which helps to smooth the profile of theresultant energy captured by the system. This effect is further enhancedby the plurality of wave energy absorbers 68 being arranged in adelta-wing arrangement since this results in each new wave frontgenerating sine wave energy profiles at the forward wave energyabsorbers 68 whilst older passing wave fronts are still interacting withmore rearward wave energy absorbers 68.

The wave energy absorbers 68 may be actively controlled in order toadjust the buoyancy stiffness of each individual absorber arrangement asit is displaced upwards or downwards in response to wave and swellformations passing by the power generating module 10.

The SSP 14 itself provides a very stable structure for the variouscomponents described since it is always aligned well with any prevailingwater current, has a low and centralised centre of gravity, benefitsfrom inherent geometric stabilities and makes use of the small waterplane area struts/flotations and heave plates.

The energy simultaneously harvested by the multiple aforementionedarrangements can be accumulated by mechanical or electrical means suchthat conditioned and smoothed energy pulses may be fed into theelectricity grid as appropriate. Example mechanical accumulators mightinclude pneumatic or hydraulic pressure accumulators or springs orflywheels etc. Example electrical accumulators might include e.g.capacitors or batteries etc. Alternatively/additionally, the harvestedenergy could be utilised on-board the module 10 to useful effect such asin the production of gas (e.g. hydrogen or oxygen) or indesalination/electrolysis operations etc.

In addition to those previously described, the present invention alsohas the advantage of allowing many moving and complex mechanical partsto remain well above the water level and away from the splash zone. Thisresults in greater expected longevity due to reduced wear and tear.

Furthermore, it will be appreciated that the described invention has theadvantage of being configurable at virtually any scale whilst also beingwell suited to being provided as either a singular unit or in a field ofseveral units.

Although particular embodiments of the invention have been disclosedherein in detail, this has been done by way of example and for thepurposes of illustration only. The aforementioned embodiments are notintended to be limiting with respect to the scope of the appendedclaims.

It is contemplated by the inventors that various substitutions,alterations, and modifications may be made to the invention withoutdeparting from the spirit and scope of the invention as defined by theclaims. For example:

Although the embodiments described within the present applicationprimarily refer to a floating arrangement provided on a body of water,the invention is not limited to being provided on a floating platformbut instead may be provided on a variety of possible foundations such ason land or ice whether the invention be directly attached to suchfoundations (in e.g. the case of a turbine directly resting on a pieceof land) or installed on vehicles or buildings (in e.g. the case of aturbine installed atop a building).

The invention may be provided with control systems for maintaining thecorrect level of buoyancy in the floating platform and/or assimilatingenvironmental and demand side data signals such that the turbineoperational efficiency and output is maximised. This may be achievedthrough pre-programmed controls, learning control algorithms or anyother appropriate control strategy as required.

In an alternative embodiment illustrated with reference to FIG. 1C, thepower generating module 210 may be provided with LIDAR sensors 212 inorder to provide the LIDAR capability previously mentioned. Furthermore,the vertical stabiliser 220 is provided with a corresponding ruddercontrol surface 221, a horizontal stabiliser 223 and correspondingelevator control surfaces 230. These surfaces allow the orientation ofthe duct or cowl 216 to be controlled in a similar fashion to the way inwhich an aircraft tail is able to control the yaw angle and angle ofattack to the oncoming airflow. Trim-tabs may also be provided to trimout any forces required to maintain the cowl 216 in the optimalorientation with respect to the prevailing wind direction.

The embodiment illustrated in FIG. 1C is also provided with externalaerodynamic vanes 225 which further facilitate aerodynamically efficientairflow over and around the cowl 216. Leading edge aerodynamic flaps 227are provided adjacent the inlet duct 222 and corresponding trailing edgeaerodynamic flaps 229 are provided adjacent the outlet duct 224. Theflaps 227, 229 may be controlled and deployed by an on-board or remotecontrolled system in response to any forward looking wind or sea statesensor information (such as the aforementioned information obtained fromthe LIDAR system).

The invention claimed is:
 1. A ducted wind turbine for flotation on a body of water comprising: a turbine rotor assembly adapted to extract kinetic energy from air flowing there past, the rotor assembly comprising a plurality of rotor blades having rotor tips at their outermost ends which define a rotor tip sweep circumference; a duct assembly at least partially surrounding said rotor tip sweep circumference; a semi-submersible base platform comprising a delta wing shaped arrangement having a plurality of discrete flotation hulls extending downwardly therefrom; fore, aft, and two flanking flotation hulls, one flotation hull being provided at or toward each corner of the semi-submersible base platform, the flotation hulls extending downwardly from the delta wing shaped arrangement and adapted to support the ducted wind turbine on a body of water; wherein the duct assembly is mounted on the base platform by way of a weathervane bearing arrangement such that the duct assembly weathervanes around the turbine rotor assembly in response to changes in wind direction; and a ducting channel being provided between a ducting inlet and a ducting outlet of the duct assembly, each of the ducting inlet and outlet having a longitudinal axis and wherein the ducting inlet and outlet are arranged such that their respective longitudinal axes intersect with one another at a redirect angle α and wherein the plurality of turbine rotor blades in the turbine rotor assembly are assembled on sets of coaxial contrary rotating hubs such that at least a primary set of rotor blades rotating in one direction and at least a secondary set of rotor blades rotating in an opposite direction are provided.
 2. A ducted wind turbine according to claim 1, wherein the redirect angle α is between around 90 to 170 degrees.
 3. A ducted wind turbine according to claim 1, wherein a rotor plane area of a first set of rotor blades and a rotor plane area of a final set of rotor blades are substantially equal to one another in order to minimize compression or expansion of air flowing through the wind turbine.
 4. A ducted wind turbine according to claim 1, wherein the area of the ducting inlet is greater than the area of the rotor plane area of the first set of rotor blades in order to create a ram effect on air passing through the turbine.
 5. A ducted wind turbine according to claim 1, wherein the area of the ducting inlet is lesser than the rotor plane area of a final set of rotor blades in order to create a diffuser effect on air passing through the turbine.
 6. A ducted wind turbine according to claim 1, wherein the ducting inlet and the ducting outlet each comprise a circular, ovoid or rectangular shaped area.
 7. A ducted wind turbine according to claim 1, wherein the ducting channel comprises at least a guide vane arrangement adapted to guide air flow through the ducting channel and into the turbine rotor assembly.
 8. A ducted wind turbine according to claim 1, wherein the inner surface of the ducting channel is aerodynamically optimised to facilitate smooth flow of air flow therethrough with minimal energy losses.
 9. A ducted wind turbine according to claim 1, wherein the outer surface of the ducting channel is aerodynamically optimised to minimise structural loads and aerodynamic turbulence on the turbine and semi-submersible base platform while enhancing air flow and promoting lower pressure across the ducting outlet and adding momentum to flow exhausted from the turbine outlet in order to aid the turbine mass air flow and energy capture.
 10. A ducted wind turbine according to claim 1, wherein the wind turbine arrangement is provided with a vertical stabiliser tail, either integrated with or separated from yet connected to, the ducted wind turbine in order to facilitate said weathervane movement.
 11. A ducted wind turbine according to claim 10, wherein the tail comprises steerable control surfaces and/or trim tabs.
 12. A ducted wind turbine according to claim 1, wherein each of the flotation hulls comprises a lower float member attached to the semi-submersible platform by way of a support strut having a small hull cross sectional area at the water surface in order to maximise the stability of the support provided.
 13. A ducted wind turbine according to claim 1, wherein the weathervane bearing arrangement comprises a substantially circular load bearing plate and a corresponding substantially circular recess provided between the wind turbine arrangement and the semi-submersible base platform such that, in use, the duct assembly weathervanes around the turbine rotor assembly.
 14. A ducted wind turbine according to claim 13, wherein the weathervane bearing arrangement is further provided with friction reducing means in order to facilitate loaded rotational movement of the duct assembly relative to the semi-submersible base platform in response to movements in the prevailing wind direction.
 15. A ducted wind turbine according to claim 1, wherein a plurality of wave energy absorbers extend from an attachment point on the semi-submersible base platform to the water such that one end of each wave energy absorber is directly or indirectly supported by the base platform and the other end is supported by buoyant engagement with the water.
 16. A ducted wind turbine arrangement according to claim 15, wherein said wave energy absorbers extend rearward from a trailing edge of the semi-submersible base platform on either side of the turbine arrangement.
 17. A ducted wind turbine arrangement according to claim 15, wherein said attachment points of the wave energy absorbers are arranged progressively rearward on the semi-submersible platform such that, in use, a wave passing the wind turbine arrangement will progressively interact with the forwardmost to rearmost wave energy absorbers in succession.
 18. A ducted wind turbine arrangement according to claim 15, wherein the wave energy absorbers are provided with an energy flotation module for buoyant interaction with the water.
 19. A ducted wind turbine arrangement according to claim 18, wherein the energy flotation module comprises a substantially semi-spherical flotation member provided at a distal end of a structural arm of the wave energy absorber.
 20. A ducted wind turbine arrangement according to claim 18, wherein the energy flotation module comprises a combined monocoque structural arm and flotation chamber.
 21. A ducted wind turbine arrangement according to claim 15, wherein the wave energy absorbers are attached to the semi-submersible platform by way of a torsional bearing arrangement comprising a first rotatable member, a second rotatable member in rotatable communication with the first rotatable member, and torsional resistance means provided between the first and second rotatable members such that when at least one of the rotatable members is rotated relative to the other rotatable member a torsional resistance to such movement is created between said rotatable members.
 22. A ducted wind turbine arrangement according to claim 1, further comprising at least a water turbine arrangement supported below the water surface by the semi-submersible platform.
 23. A ducted wind turbine according to claim 1, further comprising a diffuser arrangement adapted to improve air flow through the turbine rotor assembly. 